passing bash array separated by comma

Question

i have bash script which do some function with website domains like following

#!/usr/bin/env bash
domain="$1";
function A(){
ping $domain -c 4
}

function B(){
host $domain
}

A;
B;

and when i run this script by doing ./script.sh whateverdomain.com it works well. BUT i heard that with array i can run the script against some of domains seperated by comma for example. like ./script.sh domain1.com,domain2.com and it will excute the whole script function against the first one then the second one and i tried the following code.

my_arr=($(echo $DOMAIN | tr "," "\n"))
d=$(for domain in "${my_arr[@]}" ; 
do echo $domain
done)

pingme(){
ping -c 4 $d
}

but it hanging and not passing each domain to variable $d so i need to define array as function and when i run the script it pass domain and execute the script functions then repeat the whole script against the second domain and so on like.

#!/usr/bin/env bash
domain="$1";

function myarray(){
# the array function which will pass the domains one by one
}

function A(){
ping $domain -c 4
}

function B(){
host $domain
}

myarray;
A;
B;

Pass the arguments separately: ./script.sh domain1.com domain2.com and iterate over the elements of "$@" in the script: for domain in "$@"; do …; done. That is the natural way to write shell scripts. Also pass the domain explicitly to the function — global variables are problematic. If you must use the comma-separated argument, then use: for domain in "${my_arr[@]}"; do pingme $domain; done — and the functions should process $1, not a global variable. Inside a function, $1 is the argument passed to the function, not to the script as a whole. — Jonathan Leffler
– Jonathan Leffler, Commented Aug 11, 2020 at 12:43
In addition to everything said above, see BashPitfalls #50 (about that particular mechanism for splitting a string into an array) and wiki.bash-hackers.org/scripting/obsolete (about the function keyword). — Charles Duffy
– Charles Duffy, Commented Aug 11, 2020 at 12:49
@JonathanLeffler if i don`t use global variable how would i define the variable in each function without running the for loop in each function ! — Emad
– Emad, Commented Aug 11, 2020 at 13:12
In the text you posted, my_arr=($(echo $DOMAIN | tr "," "\n")) is the only place I see $DOMAIN capitalized. — Paul Hodges
– Paul Hodges, Commented Aug 11, 2020 at 13:20

Jonathan Leffler · Accepted Answer · 2020-08-12 00:18:27Z

2

^{Converting comments into an answer.}

The natural way to write shell scripts is to pass the arguments separately:

./script.sh domain1.com domain2.com

and iterate over the elements of "$@" in the script, passing the domain names explicitly to the function (as shown) — global variables are just as problematic in shell scripts as in other programming languages.

#!/usr/bin/env bash

A() { ping "$1" -c 4; }
B() { host "$1"; }

for domain in "$@"
do
    A $domain
    B $domain
done

If you must use the comma-separated argument, then use:

domains=($(echo "$1" | tr "," "\n"))

pingme() { ping "$1" -c 4; }

for domain in "${domains[@]}"
do
    pingme $domain
done

and (as before) the function should process $1, not a global variable.

Inside a function, $1 is the first argument passed to the function, not what's passed to the script as a whole.

Note that in the original code, none of the semicolons is needed. In the code I wrote, the semicolons before the close braces are needed because I lazily wrote the functions on a single line (because they are so simple — I would probably not use functions for such simple commands, especially as they're each only invoked once in the script). If they were spread over three or four lines, the semicolons would not be needed.

A()
{
    ping "$1" -c 4
}

Also, you don't need to use the keyword function — and it is generally regarded as a bad idea to do so. As Charles Duffy noted in a comment, the Bash Hackers wiki indicates you should not use function.

answered Aug 12, 2020 at 0:18

Jonathan Leffler

759k145 gold badges961 silver badges1.3k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Emad Over a year ago

Thanks for clarification, it works when i get the whole thing together. one more thing , i use global variable as following

domain="$1"; mkdir -p $(pwd)/$domain-$(date +"%H-%M-%S-%d-%m-%y"); WORKING_DIR="$(pwd)/$domain-$(date +"%H-%M-%S-%d-%m-%y")";

because my script contains more than one function so i need to pass variable $domain in each function which would be certain char because it is timed as u see but in general for loop worked as u described. Thanks Sir

Collectives™ on Stack Overflow

passing bash array separated by comma

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related